A galaxy ten times the mass of the Milky Way is preparing to become a quasar

One of the fundamental questions in astronomy is how galaxies formed over 13 billion years ago and have evolved since then. A common feature astronomers have noted is that most galaxies appear to have supermassive black holes (SMBHs) at their centers – like Sagittarius A*, the ~4 million solar mass SMBH at the center of the Milky Way. These monster black holes occasionally swallow nearby gas, dust, and stars, releasing excess energy as powerful relativistic jets. This phenomenon, in which a galaxy’s center outshines the stars in the disk, is known as an active galactic nucleus (AGN) or quasar.

In a recent study, an international team of astronomers led by the European Southern Observatory (ESO) discovered a galaxy in the early Universe that could reveal more about this evolution. Using the Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, they observed a swarm of galaxies orbiting a very bright and strongly star-forming galaxy in the early Universe. These observations provide new insights into how extraordinarily bright galaxies grow and evolve into quasars, emitting powerful beams of light across the observable universe.

The research was led by Michele Ginolfi, a research fellow at the European Southern Observatory (ESO) in Garching, Germany. He was joined by researchers from the National Institute for Astrophysics (INAF), the Cavendish Laboratory, the Kavli Institute for Cosmology, the Max Planck Institute for Astrophysics (MPIA), the Cosmic Dawn Center (DAWN), the Niels Bohr Institute (NBI), the Paris Institute for Astrophysics (IAP) and several universities. The paper describing their findings recently appeared in the journal nature communication.

Originally observed in 1963, quasars (short for quasi-stellar objects) got their name because they resembled stars but were bright in the radio spectrum. Today the term is used to describe all supermassive black holes that are particularly bright because they consume surrounding gas, dust, and stars. Today, many details about how galaxies transition from “normal” to quasar are still unknown. To learn more about this process, Ginolfi and his colleagues studied W0410-0913, one of the brightest, most massive, and most gas-rich galaxies observed in the early Universe.

Located about 12 billion light-years from Earth, this galaxy appears to astronomers to be about 1 billion years after the Big Bang. What makes W0410-0913 so bright is the heating of the dust by its central black hole and surrounding stars. As a result, this type of galaxy appears particularly bright in the infrared spectrum, leading to the designation “hot dust-obscured galaxies” (aka “hot DOGs”). As Ginolfi recently explained in a press release from the Niels Bohr Institute:

“Some galaxies are believed to go through a phase where they are very dusty and very ‘active’ in terms of star formation and the accretion of gas onto their central supermassive black holes before they evolve into full-grown quasar . We set out to design an experiment to learn more about this transition phase.”

Because the evolution of galaxies is linked to their environment, Ginolfi drew on data obtained from the Multi Unit Spectroscopic Explorer (MUSE) instrument on the Very Large Telescope (VLT) in Chile, which enabled them to study a region which is 40 times larger than the galaxy itself. They then consulted archival data obtained from the ALMA array, which allowed them to measure the internal motion of gas in W0410-0913. As Peter Laursen, a researcher at the Cosmic Dawn Center in Copenhagen and co-author of the study, explained:

“The observations showed that W0410-0913 is surrounded by a swarm of no fewer than 24 smaller galaxies. The cool thing about the MUSE instrument is that not only can we measure their position in the sky, but also their distance along our line of sight. In other words, we can measure their 3D positions.”

This implies that W0410-0913 is in a region at least 10 times denser than the average Universe. This wasn’t entirely unexpected since hot dogs theoretically live in dense environments. Furthermore, W0410-0913 was already ten times as massive as our galaxy when the Universe was about 1/8 the current age of the Universe. Achieving this growth in such a short time and feeding a supermassive black hole to reach this level of brightness would require a significant amount of feedstock.

This is consistent with established theories of how massive galaxies grow by accumulating gas and gravitationally merging with satellite galaxies. In the dense environment that occupied W0410-0913, the research team expected it to undergo interactions and mergers with other galaxies at a very high rate. They also assumed that the galaxy’s interior would be a chaotic jumble of swirling clouds of gas and stars. In that regard, they were surprised when the ALMA observations showed that W0410-0913 appeared to be unperturbed by interactions with its neighbors at all.

In fact, the ALMA observations showed that the gas and stars spun in an orderly fashion around the central black hole, even though it was moving at an incredible speed – 500 kilometers per second (1.8 million km/h; 1.12 million mph )! Ginolfi said:

“When we couple the results from the two very different telescopes, we see a picture of how the most massive and dustiest galaxies can evolve. This type of galaxies, a crucial stage in the transition from a dusty and star-forming galaxy to a quasar, tend to grow in very dense environments. However, despite the expected frequent mergers with other galaxies, these gravitational interactions are not necessarily destructive – they feed the central galaxy and churn up the gas a bit, but leave it practically intact. A bit like throwing small pebbles at a solid pane of glass: you can scratch them but not break them…“

These observations shed light on how galaxies in the early Universe evolved into what we see today with the Milky Way’s neighbors. It also provides the first clues to the processes driving the evolution of Hot DOGs, an extreme and rare population of galaxies in our Universe. From what Ginolfi and his colleagues have gathered with the VLT and ALMA, these galaxies grow in special, dense habitats, but are still able to interact gently with their companions. In the coming years there will be many opportunities for follow-up observations of these and other early galaxies with next-generation telescopes.

This includes the James Webb Space Telescope (JWST) and the successor of the Venerable Hubble – the Nancy Grace Roman Space Telescope (RST) – scheduled to start in 2027. There are also the next-generation ground-based telescopes that will join the VLT and ALMA, including ESO’s Extremely Large Telescope (ELT) and other 30-meter (ft)-aperture instruments like the Giant Magellan Telescope (GMT) and the Thirty Meter Telescope (TMT). Knowing the intricacies of how galaxies evolve is also expected to provide new insights into dark matter and dark energy, leading to more comprehensive models of cosmic evolution.

Further reading: Neils Bohr Institute, Nature